Last Portion of Original Floor

Floor of unnamed crater inside the larger Humboldt crater. LROC NAC M113440414L. Image width is 765 m. Illumination is from left side of the image, incidence angle 54° [NASA/GSFC/Arizona State University].

Humboldt crater is a large (207 km diameter) floor-fractured crater, located on the eastern limb as seen from the Earth, about 760 km south of Mare Smythii. The edges of its fractured-floor are partially covered by dark mantle deposits, which are suspected to be pyroclastic in origin.

Today's Featured Image is the bottom of an unnamed crater, located at the western edge of the Humboldt crater floor (the crater diameter is about 5.7 km). The boomerang-shaped flat area in the center of this image is the original floor, surrounded by continuous slopes from the crater rim.

The initial shape just after the impact event is generally thought to be a symmetric bowl-shape, with mass wasting gradually modifying the crater cavity. Especially for the small craters on the Moon, bowl-shaped cavities are transformed by this process into inverted cone shapes. This unnamed crater in Humboldt may be undergoing such a process now to become a complete cone shape at some point in the future. If so, we are fortunate to observe its original floor before complete burial obscures it from view.